In recent years, in liquid crystal displays, organic and inorganic electroluminescence devices, electronic papers, etc., a film or a glass substrate having a transparent conductive layer has been used as an electrode on the light-emitting side (see, for example, Patent Documents 1 to 4).
The transparent conductive layer is generally composed of an indium tin oxide, a zinc oxide, a tin oxide, etc., and has to be thick and uniform to achieve low resistance. Thus, the transparent conductive layer is disadvantageous in low light transmittance, high cost, and that a high temperature treatment is needed in the formation process. Particularly in the case of forming the layer on the film, the resistance can be lowered only to a limited extent.
In view of reducing the problem, proposed are a method containing adding a conductive component such as a metal wire to a transparent electrode layer (Patent Document 2), a method containing forming a busline of a conductive metal on a transparent electrode layer (a transparent positive electrode substrate) (Patent Documents 1 and 3), and a method containing forming a network-patterned metal wire structure on a transparent electrode layer (an upper electrode) (Patent Document 5).
The methods described in Patent Documents 1 and 2, etc., which include vapor-depositing or sputtering a transparent electrode layer of a conductive metal, such as an ITO (Indium Tin Oxide) layer, to increase conductivity, are poor in productivity, and need improvement on this point. Furthermore, in the method using the busline, the number of processes is increased, thereby resulting in high cost.
In Patent Document 5, an ITO layer is vapor-deposited to increase conductivity. However, there are fears of depletion of the ITO, and thus an alternative material is demanded. In addition, great loss is disadvantageously caused in the vapor deposition process.
In a method disclosed in Patent Document 6, a substantially transparent conductive layer, which contains an intrinsically conductive polymer and a conductive metal nonuniformly distributed therein, is formed on a support. The conductive layer per se acts as a conductor, and the nonuniformly distributed conductive metal is generated by a photographic processing. However, the method is unsatisfactory for the purpose of mass-producing a transparent conductive film having high light transmittance and low surface resistance at low cost.
Recently flexible displays using organic EL and electronic paper technologies, etc. have been actively studied, and a flexible transparent conductive film is needed in the flexible display. When the above transparent conductive layer is bent, the layer is finely cracked, resulting in deterioration in conductivity. In recent years, transparent conductive resins (such as PEDOT/PSS) and nanotechnology materials (such as carbon nanotubes, metal nanowires, and metal nanorods) have been actively studied as flexible conductive material. However, the materials cannot alone achieve a low resistance as the ITO layer.    Patent Document 1: Japanese Laid-Open Patent Publication No. 08-180974    Patent Document 2: Japanese Laid-Open Patent Publication No. 09-147639    Patent Document 3: Japanese Laid-Open Patent Publication No. 10-162961    Patent Document 4: Japanese Laid-Open Patent Publication No. 11-224782    Patent Document 5: Japanese Laid-Open Patent Publication No. 2005-302508    Patent Document 6: Japanese Laid-Open Patent Publication No. 2006-501604 (PCT)